Tiny motor could power artery-cruising robots

A lab bench prototype of the new motor. Applying voltage to the piezoelectric material sets up vibrations that the stator translates into a rotation of the ball – a design that could be shrunk further to drive small robots inside the body, its creators say

(Image: IOP/Monash University)

Surgical instruments have been shrinking for years as keyhole surgery has become the norm for many operations. Now a new tiny mechanical motor could help continue this miniaturisation process by powering surgical robots small enough to freely roam the body.

The common procedure of feeding a catheter tube through a patient’s blood vessels can make many operations less invasive than traditional open surgery techniques, but some arteries are just too small to be safely reached this way.

So engineers from the University of Monash in Victoria, Australia, have built a motor for a microbot that they believe could be used to reach the narrower straits of the circulatory system, such as arteries in the brain or retina.

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Flailing tail

The new motor is not much more than a millimetre long and was named Proteus after the vessel that travelled through the bloodstream of a stricken scientist in the1966 film, Fantastic Voyage.

The device is powered by a piezoelectric material, which vibrates in response to an applied electric field. A spiral rod absorbs those vibrations and translates them into rotational forces that spin a tiny stainless-steel ball.

That motion could be put to work to rotate a whip-like tail over a thousand times a second, say the team, in a similar style to the beating flagellum of a sperm cell. The performance of the motor was measured using high-speed camera footage.

The researchers calculate this could propel a microbot through the blood stream with enough power for it to navigate through an artery, in the direction of blood flow, at speeds of about 6 centimetres per second.

Batteries not included

The simplicity of the way piezoelectric materials turn electricity into motion has attracted engineers trying to build small motors before. But until now such designs have been more complex and delicate than the new design, say the researchers, which has the potential to be scaled down even further.

The Monash team is currently working to eliminate other kinds of movement in the design, such as bending, that could distort the rotational motion.

But sending the motor into even the body of an animal is still a distant prospect. It would need to be teamed up with a suitably small power pack and sensing capabilities to be of any use.